let x = {y = 123}
assert($"" == "")
assert($"\{\}" == "{}")
assert($"{3}" == "3")
assert($"\\{0}\\{1}" == "\\0\\1")
assert($"{3}{4}" == "34")
assert($"{"3"}{"4"}" == "34")
assert($"abc{123}def" == "abc123def")
assert($"abc{          123}def" == "abc123def")
assert($"abc{          123  -    3         }def" == "abc120def")
assert($"abc{x.y}\u20" == "abc123 ")
assert($"{x["\u79"] == 123}" == "true")
assert($"'" == "'")
assert($"\\\\" == "\\\\")
assert($"\t\n" == "\t\n")
assert($"/" == "/")
assert($"\}{{s="qwe"}["s"]}\{" == "}qwe{")
